L-ascorbic acid has many known biological functions from enzymatic co-factor to "sparing" agent against vitamin E depletion. See, for example, Englard and Seifter, "The Biochemical Functions of Ascorbic Acid", Ann. Rev. Nutri. 6:365-406, (1986); Kunert and Tappel, "The Effect of Vitamin C on in vivo Lipid Peroxidation in Guinea Pigs as Measured by Pentane and Ethane Production, Lipids; 18:271-74 (1983). The latter function may partly account for its "anti-oxidant" status. Additionally, at higher concentrations, ascorbic acid is known to react with both the superoxide and hydroxyl radicals. Superoxide and the subsequently generated hydrogen peroxide and hydroxyl radical are oxygen-containing free radicals now known to be generated in vivo under a variety of normal and pathological conditions. Quite simply, these radicals have been implicated as causative agents for everything from sunburn to aging. These radicals destroy lipid membranes, break down DNA, inactivate enzymes and so forth. An immense amount of work has been done in the last two decades documenting the deleterious behavior of oxygen radicals. Several recent texts on the subject include:
Oxy-radicals in Molecular Biology & Pathology, D. Cerutti, I. Fridovich, J. McCord, eds., (Alan R. Liss, Inc. New York, 1988);
Biological Role of Reactive Oxygen Species in Skin, O. Hayaishi, S. Inamura, Y. Mayachi, eds. (Elsevier Press, New York, 1987);
Free Radicals Aging and Decenerative Diseases, J. E. Johnson, Jr., R. Walford, D. Harmon, J. Miguel, eds. (Alan Liss, Inc., New York, 1986);
Free Radicals in Biology and Medicine, B. Halliwell and J. M. C. Gutteridge, eds. (Clarendon Press, Oxford, 1985); and
Oxidative Stress Helmut Sies, ed. (Academic Press, 1985).
Also addressing the subject are several symposia, including "Oxygen Radicals and Tissue Injury" Proceedings from an Upjohn Symposium (April, 1987); and "Oxygen Free Radicals", Proceedings from National Heart, Lung & Blood Institute (National Institute of Health, Washington, D.C., December 1987).
L-ascorbic acid rapidly undergoes oxidative degradation due to the ascorbate anion's propensity to act as a reductant. The one-election oxidation product (dehydroascorbate free radical) tends to disproportionate, forming another ascorbate molecule and the two-electron oxidation product, dehydroascorbate, which is extremely unstable in aqueous solutions and breaks down to ultimately form species such as L-threonic acid and oxalic acid which are not beneficial for treating skin conditions.
The literature describes ascorbic acid compositions formed by using a very low weight percent ascorbic acid, or a nonaqueous solvent, or by using derivatives of ascorbic acid, usually in a solution buffered to a pH above 4.0. See, for example, Takashima et al, "Ascorbic Acid Esters and Skin Pigmentation," Am. Perfumer & Cosmetics 86: 29 (July 1971) (esterifying the hydroxyl group to form ascorbic acid-3-phosphate and maintaining an alkaline pH); Ciminera and Wilcox, "Stable Ascorbic Acid Solution for Parenteral Use", J. Am. Pharm. Assoc. Sci. Ed. 35:363 (1946) (buffering an aqueous solution with an alkaline sodium salt). See also U.S. Pat. No. 4,367,157 which discloses stabilizing an aqueous ascorbic acid solution by adding monothioglycerol and maintaining the pH between 4 and 7; U.S. Pat. No. 2,400,171 which discloses stabilizing ascorbic acid by converting it to its calcium or zinc salt and preferably maintaining the pH at 7 to 7.3; U.S. Pat. No. 2,442,461 which discloses stabilizing calcium ascorbate by adding an aliphatic thiocarboxylic acid and maintaining the pH between 5.2 and 5.6; U.S. Pat. No. 2,585,580 which discloses stabilizing ascorbic acid with thio-sugars and maintaining the pH between 4.0 and 6.5; and U.S. Pat. No. 4,372,874 which discloses actually removing the water to below 0.5 wt % by using a desiccant. In many cases, these techniques have been successful in obtaining stable solutions but have been reasonably expensive and have yielded a product with less desirable properties than ascorbic acid in its unmodified form.
The prior art methods of preparing a stable L-ascorbic acid solution are more expensive and require immediate use of the entire package once exposed to air.
Therefore, there is a need for producing unit dosages for single applications without causing degradation of an entire package.
U.S. Pat. No. 5,587,149 to Punto et al. discloses topical vitamin C emulsions which are packaged in gelation capsules. Since they are packaged in capsules, low amounts of water and vitamin C are utilized. To increase solubility without increase in water, mineral oil is utilized. Mineral oil has the disadvantage when used on acne or acne related diseases. Also, some commercial mineral oils contain benzene hydrocarbons.